Female Pronghorn Research Articles

Relating gut microbiome composition and life history metrics for pronghorn (Antilocapra americana) in the Red Desert, Wyoming.

Host microbial communities (hereafter, the 'microbiome') are recognized as an important aspect of host health and are gaining attention as a useful biomarker to understand the ecology and demographics of wildlife populations. Several studies indicate that the microbiome may contribute to the adaptive capacity of animals to changing environments associated with increasing habitat fragmentation and rapid climate change. To this end, we investigated the gut microbiome of pronghorn (Antilocapra americana), an iconic species in an environment that is undergoing both climatic and anthropogenic change. The bacterial composition of the pronghorn gut microbiome has yet to be described in the literature, and thus our study provides important baseline information about this species. We used 16S rRNA amplicon sequencing of fecal samples to characterize the gut microbiome of pronghorn-a facultative sagebrush (Artemisia spp.) specialist in many regions where they occur in western North America. We collected fecal pellets from 159 captured female pronghorn from four herds in the Red Desert of Wyoming during winters of 2013 and 2014. We found small, but significant differences in diversity of the gut microbiome relative to study area, capture period, and body fat measurements. In addition, we found a difference in gut microbiome composition in pronghorn across two regions separated by Interstate 80. Results indicated that the fecal microbiome may be a potential biomarker for the spatial ecology of free-ranging ungulates. The core gut microbiome of these animals-including bacteria in the phyla Firmicutes (now Bacillota) and Bacteroidota-remained relatively stable across populations and biological metrics. These findings provide a baseline for the gut microbiome of pronghorn that could potentially be used as a target in monitoring health and population structure of pronghorn relative to habitat fragmentation, climate change, and management practices.

Temporal and Spatial Influences on Fawn Summer Survival in Pronghorn Populations: Management Implications from Noninvasive Monitoring.

Monitoring vital rates allows managers to estimate trends in growth rates of ungulate populations. However, connecting the influence of nutrition on ungulate demography is challenging. Noninvasive sampling offers a low-cost, low-effort alternative for measuring nutritional indices, allowing for an increased understanding of the mechanistic relationships between environmental factors, nutrition, and specific population vital rates. We examined the temporal influence of intrinsic and extrinsic factors on pronghorn (Antilocapra americana) fawn recruitment. We collected fresh fecal samples from adult female pronghorn in five subpopulations spanning three sampling periods associated with critical maternal life-history stages (late gestation, early lactation, breeding season) for 2 years to investigate both intra- and interannual influences. Intrinsic factors were fecal glucocorticoid metabolites (FGMs), nutritional indices (fecal nitrogen (FN) and 2,6-diaminopimelic acid (DAPA)), and dietary composition (protein intake of forbs, graminoids, legumes, other, shrubs), while the extrinsic factor was vegetative greenness (normalized difference vegetation index (NDVI)). We found variations in DAPA, protein intake of forbs, variation in forb protein intake, and protein intake of legumes during late gestation positively influenced fawn recruitment. Fecal nitrogen during early lactation showed the strongest positive influence on the recruitment of any measured parameter. Finally, breeding season NDVI and the variation in DAPA values positively influenced the subsequent year's fawn recruitment. Our longitudinal study enabled us to investigate which parameter was most important to specific periods of fawn development and recruitment. We combined the results across five subpopulations, but interpretation and subsequent management decisions should be made at the subpopulation level such that pronghorn subpopulations with low recruitment can be positively influenced by increasing nitrogen on the landscape available to adult females during the early lactation period. As the use of noninvasive monitoring methods continues to expand, we believe our methodologies and results can be broadly applied to other ungulate monitoring programs.

Seasonal shifts in pronghorn antelope (Antilocapra americana) diets under a new lens: Examining diet composition using a molecular technique.

Foraging is one of the most fundamental activities contributing to the maximization of an animal's fitness, and thus herbivores must optimize their diet selection and intake to meet their nutrient demands for survival, growth, and reproduction. Using plant DNA barcoding, we determined diet composition of five subpopulations of adult female pronghorn antelope (Antilocapra americana) grazing rangelands in southern and southeastern Idaho, USA. Fecal samples were collected for two years (2018-2019), and across metabolically-important adult female life history stages (late gestation, early lactation, breeding season). Plant DNA barcoding yielded 137 detected species within pronghorn diets across subpopulations and sampling periods with forbs being the most abundant. Pronghorn dietary functional group composition ranged from 52.2-60.3% from forbs followed by shrubs (22.6-28.2%), graminoids (8.7-15.7%), and legumes (5.5-9.6%). Dietary protein intake was also highest from forbs and ranged from 32.4-62.4% followed by graminoids (1.2-43.1%), shrubs (18.7-21.3%), and legumes (2.6-7.4%). We found significant intra- and interannual differences in the mean number of genera-based plant detections in pronghorn diets. Dietary protein intake of cultivated legumes (e.g., alfalfa [Medicago sativa] and sainfoin [Onobrychis viciifolia]) was lower than expected, ranging from <1.0-30.8%, suggesting that even within an agricultural-dominated landscape, factors other than plant nutritional composition contributed to pronghorn diets. Although the plant DNA barcoding technique exhibits limitations, it demonstrated potential for elucidating pronghorn dietary species richness, particularly for plants consumed in small proportions, as well as for observing temporal fluctuations in functional group composition and dietary protein intake explained through the interplay between environmental factors, plant chemical composition, and the animals' physiological needs.

Influence of cropland on resource selection by pronghorn

AbstractPronghorn (Antilocapra americana) are a grassland specialist that have experienced a &gt;60% reduction in their historical range due to habitat fragmentation and encroachment of woody vegetation. Pronghorn populations are increasing in the Texas Panhandle despite conversion of grassland to cropland (27–43% of the regional landscape) and associated fragmentation. We hypothesized that pronghorn avoid cropland when selecting seasonal home ranges and avoid cropland within their home ranges. We captured 64 adult pronghorn of equal sex ratios in both the High Plains (n = 32) and Rolling Plains (n = 32) ecoregions of Texas, USA, during February 2017 and fitted them with iridium satellite global positioning system (GPS) collars. We collared 27 additional pronghorn in 2018 to account for mortalities and collar failures. We estimated resource selection functions for the High Plains and Rolling Plains populations using mixed‐effects logistic regression at the home range (second order) and within home range (third order) scales separately for each ecoregion and season (fawning, summer, rut, and winter). Our hypothesis that pronghorn avoid cropland was supported in the Rolling Plains ecoregion at the home range scale; otherwise, cropland was inconsistently and seasonally important in resource selection. Furthermore, pronghorn often avoided paved roads more strongly than cropland. At the home range scale during 2017–2019, female pronghorn in the High Plains selected cropland during rut and winter. Males exhibited weak selection for cropland during rut. Within home ranges in the High Plains, female pronghorn avoided cropland during fawning in 2017, during rut in 2017 and 2018, and during winter 2019 but selected areas closer to cropland in winter 2017 and fawning 2018. Males selected areas farther from cropland during all sampling dates in 2017 and winter 2019. Avoidance and selection of cropland within home ranges also varied among seasons and years in the Rolling Plains. Overall, pronghorn avoided cropland when selecting home ranges in the Rolling Plains and cropland was otherwise inconsistently and only seasonally important in resource selection at the home range and within home range scales. We speculate that loss of pronghorn habitat to cropland in the High Plains and Rolling Plains of Texas may outweigh temporary nutritional benefits from seasonal use of crops.

Spatiotemporal risk factors predict landscape‐scale survivorship for a northern ungulate

AbstractEffective wildlife conservation requires decomposing the drivers of population dynamics for species affected by anthropogenic habitat alterations. Ungulates are often the focus of management actions to restore habitat and maintain connectivity as they are sensitive to landscape disturbances. We used Bayesian proportional hazards models to assess anthropogenic risk factors that could potentially predict landscape‐scale survivorship for pronghorn (Antilocapra americana) in the Northern Sagebrush Steppe ecosystem, where extensive habitat alterations occurred from the conversion of native sagebrush grasslands to agricultural lands. Using 170 adult female pronghorn monitored from 2003 to 2011, we tested the importance of linear features (road and fence densities) and forage productivity (maximum decadal normalized difference vegetation index [NDVI]) for spatiotemporal pronghorn mortality risk, while accounting for a seasonally varying proxy of snow depth. We found moderate support for the effects of linear features on mortality risk as coefficient estimates translated to predicted declines in survivorship of 27.1% over the observed range of road densities (0–1.4 km/km2) and 11.8% over the range of fence densities (0–6.1 km/km2) encountered by pronghorn. Our results also suggested that agricultural areas could act as ecological traps for pronghorn, based on mortality risk increasing by a factor of 14.3% with every 0.1 increase in maximum decadal NDVI in summer (range = 0.38–0.73). Like our previous findings, we found considerable support for the effects of average depth (in centimeters) of snow water equivalent (SWE; SWE depth = snow depth × snow density/water density) within pronghorn seasonal ranges, with mortality risk increasing by 45.7% with every 1 cm increase in SWE depth (range = 0–5.37 cm). We then developed the first broadscale, spatially explicit map of predicted annual pronghorn survivorship based on anthropogenic features and environmental gradients to identify areas for conservation and habitat restoration efforts. These efforts to highlight anthropogenic risk factors on the landscape will hopefully support conservation and habitat restoration for pronghorn populations at the northern periphery of their range.

Wind-energy development alters pronghorn migration at multiple scales.

Migration is a critical behavioral strategy necessary for population persistence and ecosystem functioning, but migration routes have been increasingly disrupted by anthropogenic activities, including energy development. Wind energy is the world's fastest growing source of electricity and represents an important alternative to hydrocarbon extraction, but its effects on migratory species beyond birds and bats are not well understood. We evaluated the effects of wind-energy development on pronghorn migration, including behavior and habitat selection, to assess potential effects on connectivity and other functional benefits including stopovers. We monitored GPS-collared female pronghorn from 2010 to 2012 and 2018 to 2020 in south-central Wyoming, USA, an area with multiple wind-energy facilities in various stages of development and operation. Across all time periods, we collected 286 migration sequences from 117 individuals, including 121 spring migrations, 123 fall migrations, and 42 facultative winter migrations. While individuals continued to migrate through wind-energy facilities, pronghorn made important behavioral adjustments relative to turbines during migration. These included avoiding turbines when selecting stopover sites in spring and winter, selecting areas farther from turbines at a small scale in spring and winter, moving more quickly near turbines in spring (although pronghorn moved more slowly near turbines in the fall), and reducing fidelity to migration routes relative to wind turbines under construction in both spring and fall. For example, an increase in distance to turbine from 0 to 1 km translated to a 33% and 300% increase in the relative probability of selection for stopover sites in spring and winter, respectively. The behavioral adjustments pronghorn made relative to wind turbines could reduce the functional benefits of their migration, such as foraging success or the availability of specific routes, over the long term.

Fence types influence pronghorn movement responses

AbstractImpediments that constrain animal movements across spatiotemporally heterogeneous landscapes can result in reduced or complete loss of access to critical resources. Across their range in North America, pronghorn (Antilocapra americana) are exposed to fences that can affect their ability to permeate the landscape, access critical resources, and respond to climatic variations. Understanding pronghorn movement responses to fences is essential for improving landscape permeability; however, prior studies provide only limited insight due to lack of information on fence characteristics and small sample sizes. Our study used hourly collar locations from adult female pronghorn in six herds in Montana, USA, and identified encounters with mapped fences to evaluate three movement responses (i.e., probability of an unaltered initial response, probability of crossing following an altered initial response, and passage time following an altered initial response) as a function of fence and landscape attributes. Based on 5581 encounters identified from movement pathways of 265 collared pronghorn and 979 km of mapped fences, we found that variability in pronghorn fence response was correlated with fence type. Woven wire fences substantially reduced unaltered initial and crossing responses and increased passage times as compared with low (i.e., average lowest wire height &lt;41 cm) or high (i.e., average lowest wire height ≥41 cm) strand fences. Both low and high strand fences elicited similar responses of being relatively permeable at the initial encounter with reduced permeability thereafter. Fence crossing probabilities following altered initial responses increased through time modestly for strand fences but only negligibly for woven wire fences, with passage times averaging approximately 14 h. Pronghorn knowledge of and fidelity to specific permeable locations along fences, which may be due to inconsistent fence and landscape characteristics along the fence stretch, likely allow some woven wire fences and most strand fences, regardless of the average lowest wire height, to be permeable. Improving landscape permeability for pronghorn should focus on removing woven wire fences, replacing woven wire fences with strand fences, and incorporating variation in the lowest wire heights into new fence designs or modifications of existing fences.

Variable effects of wind‐energy development on seasonal habitat selection of pronghorn

AbstractIn the face of climate change, wind energy represents an important alternative to oil and gas extraction to meet increasing energy demands, but it has the potential to disrupt wildlife populations. Because behavioral adjustments, such as altered habitat selection, are a primary way that long‐lived species respond to novel disturbances, we evaluated effects of wind energy development on pronghorn (Antilocapra americana) space use and habitat selection. Using data from GPS‐collared female pronghorn in the Shirley Basin of south‐central Wyoming, USA, we tested four potential effects of wind turbines on pronghorn space use during the summer and winter: (1) displacement away from wind turbines, (2) increase in size of home ranges, (3) short‐term avoidance behavior within home ranges, and (4) changes in avoidance behavior within home ranges over time. We monitored 166 individuals over five summers (2010, 2011, 2018, 2019, and 2020) and 142 individuals over five winters (2009/2010, 2010/2011, 2011/2012, 2018/2019, and 2019/2020) and used resource selection functions to evaluate selection relative to turbines after controlling for other habitat factors, such as snow depth. Although a lack of consistent negative effects of wind turbines on pronghorn across years suggested that wind energy development may have less severe and more intermittent effects on pronghorn than oil and gas development has had on other ungulates, there was a trend toward increased displacement during the study and behavioral avoidance was apparent for individuals in close proximity to turbines. However, pronghorn were highly variable in their fine‐scale habitat selection, across both individuals and years, which could make effects of wind energy development difficult to detect. Nevertheless, some individuals, particularly those close to wind‐energy facilities, did avoid turbines, which could translate to population‐level behavioral or demographic changes over time and affect the resilience and stability of the population. Over time, the accumulation of development, including wind turbines, roads, and fences, can both limit movement and fragment habitat, potentially reaching a critical threshold beyond which populations are negatively impacted.

Barrier Behaviour Analysis (BaBA) reveals extensive effects of fencing on wide‐ranging ungulates

Abstract As human activities expand globally, there is a growing need to identify and mitigate barriers to animal movements. Fencing is a pervasive human modification of the landscape that can impede the movements of wide‐ranging animals. Previous research has largely focused on whether fences block movements altogether, but a more nuanced understanding of animals' behavioural responses to fences may be critical for examining the ecological consequences and prioritizing conservation interventions. We developed a spatial‐ and temporal‐explicit approach, Barrier Behaviour Analysis (BaBA, available as an r package), to examine individual‐level behaviours in response to linear barriers. BaBA classifies animal‐barrier encounters into six behaviour categories: quick cross, average movement, bounce, back‐and‐forth, trace and trapped. We applied BaBA to wide‐ranging female pronghorn Antilocapra americana and mule deer Odocoileus hemionus in an area of western Wyoming, USA, with &gt;6,000 km of fencing. We found both species were extensively affected by fences, with nearly 40% of fence encounters altering their normal movements, though pronghorn were more strongly affected than mule deer. On average, an individual pronghorn encountered fences 250 times a year—twice the encounter rate of mule deer. Pronghorn were more likely to bounce away from fences, whereas deer engaged in more back‐and‐forth, trace and average movement near fences. We aggregated these behavioural responses to demonstrate how BaBA can be used to examine species‐specific fencing permeability and to identify problematic fence segments in order to guide fence modification or removal. Synthesis and applications. Our work provides empirical evidence on how fences affect wildlife movement. Importantly, Barrier Behaviour Analysis (BaBA) can be applied to evaluate other linear features (such as roads, railways and pipelines) and habitat edges, enhancing our ability to understand and mitigate widespread barrier effects to animal movement.

Annual Pronghorn Survival of a Partially Migratory Population

ABSTRACTThe importance of conserving migratory populations is recognized across a variety of ungulate taxa, yet the demographic benefits of migration remain uncertain for ungulate populations that exhibit partial migration. We hypothesized that migratory pronghorn (Antilocapra americana) would experience greater survival compared to residents by moving longer distances to avoid severe winter weather and access higher quality forage. We used a Bayesian time‐to‐event approach to analyze the fates of 175 radio‐collared adult female pronghorn monitored over 8 biological years (2004–2011) in the Northern Sagebrush Steppe ecosystem. Annual survivorship of migratory pronghorn was 7% higher on average compared to residents but not statistically different. Migratory pronghorn had higher survivorship in summer and winter compared to residents, and few mortalities were observed during the short autumn and spring migration periods. Mortality risk for both movement tactics intensified under more severe winter weather; winter weather severity alone best explained annual pronghorn mortality risk. The top model predicted survival rates to decline on average by 56% over the range of observed winter climatic conditions. To minimize human impacts to pronghorn during extreme climatic events, we recommend working with transportation departments and land managers to enhance pronghorn crossings of roads and railroads, and landholders to modify fences to wildlife‐friendly standards. © 2020 The Authors. Journal of Wildlife Management published by Wiley Periodicals, LLC on behalf of The Wildlife Society.

Pronghorn Winter Resource Selection Before and After Wind Energy Development in South-Central Wyoming

Few studies have evaluated the response of ungulate populations to wind energy development. Recent demand for wind-generated electricity coupled with a tendency for wind-energy facilities to be sited within suitable pronghorn (Antilocapra americana) winter range make this a critical issue for conservation of this icon of western North America. We evaluated pronghorn response to wind energy development at the winter home range scale, as well as within individual winter home ranges using data collected from 47 adult female pronghorn equipped with Global Positioning System transmitters. At both scales, we developed separate resource selection models for pronghorn before (winter 2010) and after (winters 2011 and 2012) development of the Dunlap Ranch wind energy facility in south-central Wyoming to evaluate the potential impacts of wind energy infrastructure on pronghorn winter resource selection. In general, pronghorn winter resource selection was correlated with greater sagebrush (Artemisia spp.) cover, lower snow depth, and lower slopes before and after wind energy development at both scales. At the larger scale, pronghorn selected home ranges closer to wind turbines during all winters. Within home ranges, pronghorn selected areas closer to future locations of wind turbines at Dunlap Ranch during 2010 before turbine erection. However, we found evidence that pronghorn avoided wind turbines in winters after development within their winter home ranges. This relationship was most evident during winter 2011, which coincided with the most severe winter of our study. Long-term replicated studies will be necessary to make inferences for pronghorn populations exposed to wind energy development in different environments and scales than we evaluated. Nonetheless, in the absence of additional information on how ungulates respond to wind energy development, our finding that pronghorn avoided wind turbines within their winter home ranges has important implications for future wind development projects, particularly in areas known to fulfill important seasonal requirements of pronghorn populations.

Across scales, pronghorn select sagebrush, avoid fences, and show negative responses to anthropogenic features in winter

AbstractPronghorn (Antilocapra americana) are endemic to western North America where they occupy expanses of grassland and sagebrush (Artemisia spp.) habitats. The Red Desert region in south‐central Wyoming, USA, has historically served as a stronghold for pronghorn populations, but many herds there have experienced declining population trends over the last two decades, concurrent with oil and natural gas development. These demographic changes and the potential for such energy development, its associated infrastructure, and other anthropogenic features including roads and fences to influence pronghorn habitat selection were the impetuses for our study. We sought to evaluate the potential effect of human‐induced disturbance on multi‐scale seasonal resource selection of 142 adult female pronghorn from 2013 to 2016 using 442 unique animal‐season‐year datasets. We utilized a traditional resource selection function to evaluate seasonal home‐range selection and a step‐selection function to assess fine‐scale, patch‐level seasonal selection. We also compared resource selection during daytime and nighttime hours with step‐selection analyses. At the seasonal home‐range scale, pronghorn selected for areas with more sagebrush during both seasons and areas farther from fences during summer. This trend was also apparent at the patch‐scale level, where pronghorn selected sagebrush‐dominant habitats and avoided crossing fences in all seasons during both day and night. Additionally at this scale, pronghorn selected areas farther from fences during daytime in summer. At the broader, home‐range scale, pronghorn selected areas with greater road density during summer, but with lower road densities and farther from wells during winter. Avoidance of anthropogenic features during winter was also observed at the finer, patch‐scale, with pronghorn selecting for increased density of roads and oil and natural gas wells during daytime in summer, but selecting areas farther from these features during daytime in winter. We recommend minimizing fencing and other forms of anthropogenic disturbance in high‐quality seasonal pronghorn habitats with high proportions of sagebrush, particularly during winter when risk‐avoidance responses may be amplified.

Classifying the migration behaviors of pronghorn on their northern range

ABSTRACTMigration functions as an adaptive strategy to improve fitness by allowing individuals to exploit spatiotemporal gradients of resources. Yet migration, especially among large ungulates, is increasingly threatened by human activities, making it necessary to understand variation in migratory behavior. We identified different movement strategies for pronghorn (Antilocapra americana) at the northern limit of the species’ range, and tested hypotheses for variation between migratory behaviors. From 2003–2010, we captured 185 female pronghorn across Alberta and Saskatchewan, Canada, and Montana, USA. We identified discrete migratory behaviors, including seasonal migration, facultative winter migration, potential post‐fawning migration, and the use of stopover sites. Fifty‐five percent of individuals undertook seasonal migrations, and we recorded the longest reported round‐trip migration for the species at 888 km. Some (22%) seasonal migrations included ≥1 stopover sites, with significantly greater use of stopovers during spring than fall. Migrants (34%) and residents (20%) undertook facultative winter migrations, with the majority (68%) undertaken by migrants. Additionally, 12% of individuals exhibited potential post‐fawning migrations. For each season, we estimated a suite of movement metrics and used multivariate statistics to compare movement similarities across migration behaviors. Correspondence analyses revealed 3 groupings of migration behavior. Spring migration was its own grouping, characterized by more sinuous and slower movements, consistent with the forage maturation hypothesis. Fall migration, facultative winter migration, and potential post‐fawning migration clustered in a single group that displayed linear, fast movements, consistent with being influenced by ecologically limited resources such as severe winters or predation avoidance. Lastly, spring and fall stopover sites were grouped together as a means to use high‐quality forage during migration, also consistent with the forage maturation hypothesis. At the northern periphery of pronghorn range, differences between migratory behaviors are influenced by various ecological factors, merit increased attention, and contribute to overall persistence. © 2018 The Wildlife Society.

Intrinsic, environmental, and anthropogenic factors related to pronghorn summer mortality

ABSTRACTPronghorn (Antilocapra americana) are an iconic wildlife species of sagebrush (Artemisia spp.) and grassland ecosystems in western North America. Over 50% of pronghorn have historically occurred in Wyoming; however, these populations have declined by nearly 30% in &lt;2 decades, concurrent with expanding energy development and prolonged drought. Research suggests adult female pronghorn, unlike other temperate ungulates, are more likely to die in summer, when body condition is lower from extreme energetic demands of reproduction, which are higher for pronghorn than other ungulates. To evaluate the potential effects of intrinsic, environmental, and anthropogenic factors on summer mortality risk, we monitored 114 adult female pronghorn equipped with global positioning system transmitters in the Red Desert region of south‐central Wyoming, USA between 2013 and 2015. We modeled mortality risk using Cox's proportional hazards regression. Summer mortality risk was influenced by intrinsic and environmental factors; mortality risk increased when individuals were in poorer body condition entering the previous winter and when they experienced greater variation in average daily snow depth during the previous winter. We did not detect an effect of the distance to and density of roads, oil and gas wells, or fences on pronghorn summer mortality. During years of increased winter severity with deep and fluctuating snow depths, managers may observe higher winter mortality and higher mortality the following summer, likely as a consequence of the energetic expense associated with winter survival and spring reproduction for female pronghorn. © 2018 The Wildlife Society.

How Pronghorn Females Avoid Inbreeding Depression

AbstractAfter a bottleneck in a closed population of pronghorn (Antilocapra americana), some inbred matings occurred, and we detected significant inbreeding depression. But inbred matings occurred less frequently than would be expected by chance. Pronghorn females chose mates after a sampling period and had complete control of the mating decision. Therefore, to discover the behavioral mechanism by which females avoided mating with close kin, we studied female movements and courtship sequences. When females moved from one harem to another in the sampling process, they did not shift to harem males of lower coancestry as they approached estrus. Rather, females progressed more slowly through the later courtship stages when the harem male was related vs. unrelated. Also, the rates of male courtship acts were higher within unrelated vs. related pairs. Some females appeared to use multiple mating as an inbreeding avoidance strategy. Our results suggested that inbreeding avoidance by female pronghorn occurred primarily by reactions to the late stages of male courtship, rather than by spatial avoidance of related males.

Seasonal Distribution and Routes of Pronghorn in the Northern Great Basin

Abstract. Pronghorn (Antilocapra americana) exhibit complex spatial and temporal variation in seasonal movements and range use across their distribution. However, knowledge of seasonal movements, routes, and distribution of pronghorn within the sagebrush-steppe of the northern Great Basin is lacking. From October 2011 to October 2013, I monitored movements of adult female pronghorn across an area of over 1.5 million hectares along the northwestern Nevada and southeastern Oregon border using GPS/VHF-equipped collars. I used 68,834 GPS locations from 32 female pronghorn to determine migration timing, seasonal distributions, individual fidelity to winter and summer ranges, and population-level routes used during the migration period. Collared pronghorn were conditionally migratory, with 65% migrating an average of 30.0 km the first year and 100% migrating an average of 39.1 km the second; one individual migrated over 160 km between summer and winter ranges. Seasonal ranges averaged 143.3 km2 during the summe...

Sub-lethal effects of energy development on a migratory mammal—The enigma of North American pronghorn

To meet societal demands for energy, ∼50,000 gas sites are developed annually in North America, among which many are in western less-developed and wildlife rich areas. To evaluate effects of increasing energy infrastructure requires sufficiently robust study designs, an onerous issue given the vastness of scale, limited funds, and an abject dearth of baseline data. Here we address these issues, first by discussion of the type of approaches needed to develop proper inference about potential effects of energy footprints, and subsequently through an empirical approach by examining the biological performances of more than 370 GPS radio-collared adult female pronghorn (Antilocapra americana). A rigorous attempt to examine if industrial development has any impact on pronghorn is based on three assumptions: (i) late-winter body mass reflects a period of inadequate food availability because winter habitat is altered; (ii) variation between population segments reflects spatial differences in food availability, increased energetic costs, or varying survival rates between gas field and non-developed sites; and (iii) reproductive correlates including physiological and immunological markers and adult survival are lower at sites varying in habitat quality. Our study area situated in one of the world’s premier wildlife regions–the southern Greater Yellowstone Ecosystem–harbors approximately 100,000 wintering ungulates, some of North America’s longest migrations, and two of the continent’s largest gas fields. We compared the response of five variables between wild pronghorn in control (not disturbed) and experimental (developed gas fields with well pads, roads, and traffic) sites—pregnancy, chronic stress, immune function, body mass, and adult survival. Despite shifts in animal movements, which included avoidance of energy infrastructure where development is occurring at the highest densities inside two of the largest natural gas fields in North America (Pinedale Anticline Project Area [PAPA] and Jonah fields) and other behavioral or ecological observations of sub-lethal effects, we failed to reject the null hypothesis that development is unrelated to parity in pronghorn biological responses. Studies intent on producing knowledge to assess whether energy development is inimical or not to ungulates will increasingly require appropriate time scales and understanding whether populations are below an expected food ceiling. Further, as with pronghorn in our study region, knowing if individuals are at the limits of their biological range (e.g. altitude) where stressful winter conditions may mask impacts of development is important.

Factors Influencing Winter Mortality Risk for Pronghorn Exposed to Wind Energy Development

Evaluating the influence of energy development on pronghorn (Antilocapra americana) winter mortality risk is particularly critical given that northern populations already experience decreased survival due to harsh environmental conditions and increased energetic demands during this season. The purpose of our study was to evaluate pronghorn mortality risk over 3 winters (2010, 2010–2011, 2011–2012) on a landscape developed in 2010 for wind energy production (Dunlap Ranch) in south-central Wyoming, United States. We obtained locational data and survival status of 47 adult female pronghorn captured and equipped with Global Positioning System (GPS) transmitters. Overall, 17 pronghorn died during winter seasons, with 76.4% (13) of deaths occurring during the winter with highest snow accumulation (2010–2011). Survival (Ŝ) was lowest in winter 2010–2011 (Ŝ = 0.53, 90% confidence interval [CI]: 0.37–0.70) and highest in winters 2010 (Ŝ = 0.97, 90% CI: 0.92–1.00) and 2011–2012 (Ŝ = 0.91, 90% CI: 0.82–1.00). We modeled mortality risk for pronghorn using Cox’s proportional hazards model inclusive of time-dependent and time-independent covariates within anthropogenic, environmental, and wind energy variable classes. Across winters, pronghorn winter mortality risk decreased by 20% with every 1.0-km increase in average distance from major roads (hazard ratio = 0.80, 90% CI: 0.66–0.98), decreased by 4.0% with every 1% increase in average time spent in sagebrush (Artemisia spp. L.; hazard ratio = 0.96, 90% CI: 0.95–0.98), and decreased by 92% with every 1 unit (VRM × 1000) increase in terrain ruggedness (hazard ratio = 0.08, 90% CI: 0.01–0.68). Pronghorn winter survival was not influenced by exposure to wind energy infrastructure; however, pronghorn survival may be impacted by larger-scale wind energy developments than those examined in our study. We recommend wildlife managers focus on conserving sagebrush stands in designated pronghorn winter range.

Differential investment in twin offspring by female pronghorns (Antilocapra americana)

Differential investment in offspring has been reported for many mammals, often in the context of the Trivers– Willard model of male-biased investment, but evidence of differential investment in pronghorns (Antilocapra americana) is largely lacking. We assessed the causes and consequences of different birth masses of littermate fawns in a pronghorn population in Oregon. The mass differential for co-twins ranged from 0% to 89% (median ¼ 8.35%). Male-biased investment explained the mass differential in opposite-sex litters but not same-sex litters. The mass differential did not result from mothers producing 1 normal-size fawn and 1 runt fawn, and the smaller fawn was not deficient in physiological condition. Only 29% of fawns survived to 8 weeks and both fawns died in 56% of litters, but co-twin mortalities were largely separate events. Mass did not confer a survival advantage when considering all fawns through age 8 weeks, but there was evidence of such an advantage when comparing fawns within litters before age 18 days. Differential investment in fawns might be a bet-hedging strategy in which the mother accepts a lower expected reproductive success in exchange for a lower variance, but neither the mean nor the variance differed between mothers of different-size (.8.35% mass differential) and similar-size (,8.35%) litters. In fact, there was evidence of increased reproductive success for mothers of different-size litters, much of which stemmed from higher survival 4–6 days after birth. Having different-size fawns reduced the chances of sequential mortality, in which a predator killed one fawn then returned to kill the other.

Group dynamics of Yellowstone pronghorn

Abstract Understanding mechanisms that influence the grouping tendencies of large herbivores is necessary to predict the influence of environmental and human factors on threatened populations. Locations of 53 adult female pronghorn (Antilocapra americana) in Yellowstone National Park during June 1999–April 2005 indicated that mean and typical group sizes and the variation in group size decreased during fawning when females secluded themselves, but became larger and more dynamic during fawn rearing and the rut and winter. Mixed-effects models indicated a strong effect of time of year on mean group sizes, with some evidence that predators negatively affected group sizes during winter. Within-animal variability (0.64) was substantially higher than between-animal variability (0.02). Pronghorn density, snow water equivalent, and predation apparently influenced variations in group size. Multiple regressions indicated effects of pronghorn density and snow water equivalent on typical group size, the size of the g...